US3813085A

US3813085A - Arrangement for regulating a choke valve in a carburetor

Info

Publication number: US3813085A
Application number: US00335697A
Authority: US
Inventors: M Nakada; H Matsumoto
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 1972-05-20
Filing date: 1973-02-26
Publication date: 1974-05-28
Anticipated expiration: 1991-05-28
Also published as: JPS4913524A

Abstract

In the mixing chamber of a carburetor a choke valve is spaced axially from a throttle valve. The carburetor includes a hot air chamber to which hot air heated by exhaust gas is admitted. Positioned within the hot air chamber is a bimetallic coil which, in response to the temperature of the hot air heated by exhaust gas, operates the choke valve. Communicating with the hot air chamber is a cylindrically shaped chamber containing a piston which is also displaced by the bimetallic coil as it operates the choke valve. On the opposite side of the piston from the hot air chamber, the cylindrically shaped chamber also communicates with the mixing chamber adjacent the throttle valve so that a negative pressure within the mixing chamber tends to displace the piston in the same direction that it is moved as the choke valve is opened. The side of the cylindrically shaped chamber in communication with the mixing chamber is connected through a valved passage to the hot air chamber so that differences in pressure on the opposite sides of the piston can be balanced during idling before the engine associated with the carburetor warms up.

Description

United States Patent Nakada et al.

[ May 28, 1974 ARRANGEMENT FOR REGULATING A CHOKE VALVE IN A CARBURETOR [75] Inventors: Masahiko Nakada; Hiroiumi Matsumoto, both of Toyota, Japan [73] Assignee: Toyota Jidosha Kogyo Kabushiki Kaisha, Toyota-shi, Japan [22] Filed: Feb. 26, 1973 [21] Appl. No.: 335,697

[30] Foreign Application Priority Data May 20, 1972 Japan 47-49545 [52] U.S. Cl 261/39 B [51] Int. Cl F02m 1/10 [58] Field of Search 261/39 A, 39 B [56] References Cited UNITED STATES PATENTS 2,942,596 6/l960 Carlson 261/39 B Primary ExaminerFrancis S. Husar Attorney, Agent, or FirmTorer, McGeady and Stanger [57] ABSTRACT In the mixing chamber of a carburetor a choke valve is spaced axially from a throttle valve. The carburetor includes a hot air chamber to which hot air heated by exhaust gas is admitted. Positioned within the hot air chamber is a bimetallic coil which, in response to the temperature of the hot air heated by exhaust gas, operates the choke valve. Communicating with the hot air chamber is a cylindrically shaped chamber containing a piston which is also displaced by the bimetallic coil as it operates the choke valve. On the opposite side of the piston from the hot air chamber, the cylindrically shaped chamber also communicates with the mixing chamber adjacent the throttle valve so that a negative pressure within the mixing chamber tends to displace the piston in the same direction that it is moved as the choke valve is opened. The side of the cylindrically shaped chamber in communication with the mixing chamber is connected through a valved passage to the hot air chamber so that differences in pressure on the opposite sides of the piston can be balanced during idling before the engine associated with the carburetor warms up.

8 Claims, 4 Drawing Figures ARRANGEMENT FOR REGULATING A CHOKE VALVE IN A CARBURETOR SUMMARY OF THE INVENTION The present invention is directed to an automatic choke associated with a carburetor and, more particularly, it is directed to an arrangement for automatically opening the choke valve in the carburetor in accordance with the relationship between the hot air temperature and the operating conditions of the engine associated with the carburetor. Specifically, the arrangement provides optimum running of the engine before it is sufficiently warmed up.

In general, automatic chokes are arranged to provide an optimum operation of the choke valve by balancing the spring force of a bimetallic coil exposed to the hot air temperature and the drawing force provided by the negative manifold pressure conditions in the engine acting on a piston also associated with the choke valve. However, when the engine is cold, the choke valve remains almost completely closed because of the considerable elastic force of the bimetallic coil. Accordingly, when the engine is operated under a light loading, such as during idling, and a large negative manifold pressure acts on the vacuum piston, it causes the choke valve to open against the spring force of the bimetallic coil. As a result, the choke effect is unsatisfactory and the fuelair mixture obtained is insufficient so that a faulty idling operation of the engine results.

Therefore, a primary object of the present invention is to provide an arrangement for improving the performance of the choke by overcoming the drawing force of the negative manifold pressure acting on the vacuum piston during idling or light-load running operation of the engine before it warms up.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated and described a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 is a schematic sectional view of a carburetor incorporating an automatic choke arrangement embodying the present invention;

FIG. 2 is an enlarged perspective view showing, in detail, a piston used in the arrangement illustrated in FIG.

FIG. 3 is an enlarged sectional view of a change-over valve, as shown in FIG. 1, in the position it assumes during idling or light-load running operation; and

FIG. 4 is a sectional view, similar to FIG. 3, however indicating the position of the change-over valve when the engine load has increased.

DETAILED DESCRIPTION OF THE INVENTION In FIG. 1 a carburetor 1 is illustrated having an axially extending mixing chamber la containing a choke valve 2 adjacent upper end and a throttle valve 3 spaced from the choke valve and located near the lower end of the mixing chamber. The carburetor also includes a hot air chamber 24 separate from the mixing chamber and having an inlet 9 through which hot air heated by exhaust gas is admitted into the hot air chamber. Positioned within the hot air chamber 24 is a spiral bimetallic coil 6 fixed intermediate its ends to the chamber and connected at its upper end, as viewed in FIG. 1, to a lever 5 which, in turn, is connected to a shaft 4 of the choke valve 2. In addition, the carburetor also forms a cylindrically shaped chamber 20 in which a vacuum piston 8 is axially displaceable. The piston 8 divides the chamber 20 into two. sides, one side communicates directly with the hot air chamber 24 and the other side communicates through a passage 12 and the opening 23 with the mixing chamber 1a at a position spaced between the throttle valve and the outlet 22 from the mixing chamber. A rod 7 is connected at its upper end to the lever 5 and extends downwardly and is connected by a pin 10 to the upper portion'of the piston 8. Accordingly, when the lever 5 moves downwardly, as viewed in FIG. 1, for opening the choke valve 2 the rod causes the piston to move axially downwardly.

A portion of the inner surface of the chamber 20 forms a passageway 11 which extends only for a part of the axial length of the chamber upwardly from its lower end. As can be seen in FIG. 1, the passageway 11 extends up to the lower portion of the piston 8. The passageway 11 provides a flow path for hot air from the hot air chamber 24 into the passage 12 when the piston is displaced axially downwardly. Connected to the hot air chamber 24 above the upper end of the chamber 20 is a by-pass pipe 13 which extends downwardly around the chamber 20 and is connected at its lower end to a change-over valve 25.

In FIG. 2 a recess 19 is shown extending axially downwardly into the piston 8 for a portion of its axial length. When the piston is moved downwardly for a certain length the recess 19 communicates with the passageway 11 so that the hot air can flow from the hot air chamber 24 into the chamber 20 and then into the passage 12.

In FIGS. 3 and 4 the change-over valve 25 is shown in detail and it includes a valve chamber 21 which communicates intermediate its ends with the lower end of the passage 13. Further, the valve chamber 21 also communicates through a small hole 15 with the mixing chamber at a location in the range of movement of the throttle valve 3. In FIG. 3 the hole 15 is shown located slightly upwardly from the idling position of the throttle valve 3. The valve chamber 21 is also connected to the passage 12 through two separate passages 13' and 13'. A spool 14 is axially slidable within the valve chamber 21 for regulating flow through the

passages

13, 13' and 13". At the end of the vacuum chamber 21 adjacent the hole 15 communicating with the mixing chamber is a spring 16 which biases the spool 14 away from the mixing chamber. As the spool 14 is axially displaced through the valve chamber 21 it provides a changeover effect closing off the passage 13' while the

passages

13 and 13" are in communication or closing off flow from the by-pass passage 13 while affording communication between the passages 13' and 13'.

As mentioned above, the recess 19 in the piston is provided so that a slight downward movement of the piston provides flow of the hot air from the hot air chamber 24 through the recess 19 into the passageway 11. Restrictions l7 and 18 are located in the passages l2 and 13', respectively, to regulate the flow through these passages.

In this arrangement, when the temperature of the hot air admitted into the hot air chamber 24 is low, the bimetallic coil 6 is contracted and closes the choke valve 2 and develops a large elastic force acting in the downward direction, as viewed in FIG. 1. However, as the bimetallic coil 6 is heated by the hot air, the coil expands, dissipating its elastic force, and causes the lever to turn the shaft 4 for opening the choke valve 2. As the lever moves in response to the contraction or expansion of the bimetallic coil, the vacuum piston 8 is moved in a similar manner. When the hot air temperature is low the vacuum piston 8 assumes an upper position within the chamber 20, however, at this time a negative manifold pressure corresponding to the running condition of the engine is also applied to the vacuum piston through the passage 12 and the chamber 20 and a force tending to move the piston downwardly is exerted and such downward movement tends to displace the lever 5 and the shaft 4 in the direction for opening the choke valve 2. Accordingly, the opening of the choke valve is determined by the balanced condition of the elastic force developed by the bimetallic coil and the drawing force exerted on the vacuum piston 8. If the vacuum piston moves downwardly a sufficient amount to place its recess 19 in communication with the passageway 11, the hot air in the hot air chamber 24 flow downwardly through the recess 19 and the passageway 11 into the cylinder 20 and the passage 12 and out through the outlet 22 of the mixing chamber in the carburetor. As a result, the difference in pressure between the upper and lower sides of the vacuum piston 8 effecting a reduction in the negative pressure or drawing force acting on the piston which tends to open the choke valve 2. When the engine is idling or operating under slow-speed conditions, the hole 15 is positioned slightly above the throttle valve 3, as shown in FIG. 3, and a pressure almost equal to atmospheric pressure acts on the righthand side of the spool 14 of the change-over valve 25 so that the spool is forced to move to the left under the biasing force of the spring 16 for establishing communication between the passages 13 and 13''. As a result, part of the hot air in the hot air chamber 24 flow into the mixing chamber la of the carburetor along a path formed by the

passages

13 and 13" and the opening 23 so that a reduction in the drawing force acting on the vacuum piston 8 is achieved in the same manner as described above.

When the engine load is increased and the throttle valve is turned in response to the depression of an accelerator pedal, not shown, the throttle valve moves into the position shown in FIG. 4 so that the hole 15 is located below the throttle valve and the negative manifold pressure acts directly on the right-hand end of the spool as viewed in FIG. 4. The negative pressure acting on the spool in this manner causes it to move in the rightward direction for shutting off the passage 13 and opening communication between the passages 13' and 13''. This arrangement has the same effect as when the passage 12 is enlarged in size, allowing the hot air, slightly greater in amount, than when passed through the passage 12 alone, to flow through the recess 19 and the passageway 11 and then through the

passages

12, 13' and 13" for increase the drawing force on the vacuum piston 8 in the same way as described above. In this particular arrangement, the negative pressure in the passage 12 also acts on the lefthand side of the spool 14, however, the pressure is far smaller than that acting on the righthand side of the spool from the hole 15 and the spring is adapted to provide only a limited amount of force for effecting the action illustrated in FIG. 3, whereby no appreciable restraint is imposed on the rightward movement of the spool 14.

As can be appreciated from the foregoing explanation, when the throttle valve is only partly opened, the change-over valve 25 acts to allow the hot air in the hot air chamber 24 to flow through the by-pass 13, however, when the vacuum piston 8 is moved slightly downwardly due to the relationship between the negative manifold pressure and the action of the bimetallic coil which varies with hot air temperature, the hot air is permitted to flow through the cylinder 20 inv the passage 12 so that the difference in pressure between the upper and lower sides of the vacuum piston 8 and the drawing force applied to the piston are reduced to limit the opening of the choke valve 2 and thereby correspondingly increase the choking effect. Further, in a situation where the hot air temperature is low and the bimetallic coil acts to close the choke valve, if the driver depresses the accelerator pedal and opens the throttle valve, the by-pass 13 is closed and a somewhat greater amount of hot air is allowed to flow through the

passages

12, 13, 13" whereby the increase in the opening of the choke valve 2 is arrested and the choking performance is enhanced.

When the hot air temperature is raised to cause expansion of the bimetallic coil 6, the vacuum piston 8 is displaced downwardly to its lowermost position for opening the choke valve to its full capacity. When this operating condition is reached, the choke valve ceases to be operated due to the influence of the hot air. By suitably selecting the diameters of the two restriction l7 and 18, the opening of the choke valve can be suited to any running condition of the engine. Thus, by means of the present invention, it is possible to obtain a fuelair mixture of such a fuel-air ratio that an optimum choking effect is obtained first during idling immediately following cold start up, or during idling or low speed operation of the engine before it is warmed up sufficiently, so that smooth operation of the engine can be obtained at all times.

While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

l. A carburetor comprising an axially elongated mixing chamber having an outlet at one end thereof, a throttle valve located in said mixing chamber, a choke valve located in said mixing chamber spaced from said throttle valve, an hot air chamber separate from said mixing chamber, said hot air chamber having an inlet for admitting hot air thereinto, heat-responsive means located within said hot air chamber and arranged to be exposed to the hot air admitted thereto, said heatresponsive means connected to said choke valve for operating said choke valve, a cylindrically shaped chamber in communication with said hot air chamber, a piston axially displaceably positioned within said cylindrically shaped chamber and connected to said heatresponsive means so that said piston is axially displaced by said heat-responsive means as said heat-responsive means operates said choke valve, a first passage connecting said cylindrically shaped chamber on the opposite side of said piston from said hot air chamber to said mixing chamber adjacent the outlet therefrom, a second passage connected between said hot air chamber and said first passage, and valve means arranged between said first and second passages and connected to said mixing chamber at a location near said throttle valve for regulating flow therethrough in response to the pressure in said mixing chamber.

2. A carburetor, as set forth in claim 1, wherein said valve means comprises a valve chamber in communication with said mixing chamber at a location near said throttle valve, said first and second passages connected to said valve chamber at positions spaced from one another, a spool positioned within and axially displaceable through said valve chamber in response to the pressure in said mixing chamber adjacent the location at which said valve chamber is connected to said mixing chamber so that the position of said spool regulates the flow through said first and second passages.

3. A carburetor, as set forth in claim 2, wherein a spring is positioned within said valve chamber for axially biasing said spool within said valve chamber.

4. A carburetor, as set forth in claim 3, wherein said second passage forms a by-pass about said cylindrically shaped chamber.

5. A carburetor, as set forth in claim 1, wherein said cylindrically shaped chamber forms a passageway ex-' tending for a portion of the length of said cylindrically shaped chamber on the side of said piston opposite said hot air chamber, said piston having an axially extending recess therein so that when said piston is axially displaced for a certain distance by said heatresponsive means when said heat-responsive means acts to open said choke valve the recess in said piston opens to said passageway in said cylindrically shaped chamber admitting a flow of hot air from said hot air chamber into said cylindrically shaped chamber on the opposite side of said piston from said hot air chamber.

6. A carburetor, as set forth in claim 1, wherein said heat-responsive means comprises a spiral bimetallic coil mounted in said hot air chamber, a lever connected at one end to said coil adjacent one of its ends and at its other end to said choke valve for opening said choke valve as the temperature of the hot air admitted to said hot air chamber increases.

7. A carburetor, as set forth in claim 6, wherein said heat-responsive means includes a rod connected at one end to said lever and pin connected at its other end to said piston for axially displacing said piston as said I choke valve is opened and closed.

8. A carburetor, as set forth in claim 1, wherein said throttle valve is located adjacent the outlet from said mixing chamber and said choke valve is positioned upstream from said throttle valve.

Claims

1. A carburetor comprising an axially elongated mixing chamber having an outlet at one end thereof, a throttle valve located in said mixing chamber, a choke valve located in said mixing chamber spaced from said throttle valve, an hot air chamber separate from said mixing chamber, said hot air chamber having an inlet for admitting hot air thereinto, heat-responsive means located within said hot air chamber and arranged to be exposed to the hot air admitted thereto, said heat-responsive means connected to said choke valve for operating said choke valve, a cylindrically shaped chamber in communication with said hot air chamber, a piston axially displaceably positioned within said cylindrically shaped chamber and connected to said heat-responsive means so that said piston is axially displaced by said heat-responsive means as said heat-responsive means operates said choke valve, a first passage connecting said cylindrically shaped chamber on the opposite side of said piston from said hot air chamber to said mixing chamber adjacent the outlet therefrom, a second passage connected between said hot air chamber and said first passage, and valve means arranged between said first and second passages and connected to said mixing chamber at a location near said throttle valve for regulating flow therethrough in response to the pressure in said mixing chamber.

5. A carburetor, as set forth in claim 1, wherein said cylindrically shaped chamber forms a passageway extending for a portion of the length of said cylindrically shaped chamber on the side of said piston opposite said hot air chamber, said piston having an axially extending recess therein so that when said piston is axially displaced for a certain distance by said heat-responsive means when said heat-responsive means acts to open said choke valve the recess in said piston opens to said passageway in said cylindrically shaped chamber admitting a flow of hot air from said hot air chamber into said cylindrically shaped chamber on the opposite side of said piston from said hot air chamber.

7. A carburetor, as set forth in claim 6, wherein said heat-responsive means includes a rod connected at one end to said lever and pin connected at its other end to said piston for axially displacing said piston as said choke valve is opened and closed.